Hydraulic brake problems

Hydraulic brake problems. The disc brake on my D2b has provided only
very limited stopping ability for a year or so now. When attempting
to put on the brakes the brake handle moves all the way back to the
stick grip. We have repeatedly attempted to eliminate air in the
system by pumping .4 fluid up through the wheel cylinder drain
nipple. We have sucked the system dry by vacuum applied, also to the
same nipple. We have checked the nipple itself for blockage. We
replaced the master cylinder. We checked the cable to make sure there
was no slack yet the abbreviated handle plunger was virtually in
contact with the piston in the master cylinder and the master cylinder
piston was moving. Nothing seems to make any difference. IT

On Mar 27, 9:34*am, Dick wrote:
Hydraulic brake problems. *The disc brake on my D2b has provided only
very limited stopping ability for a year or so now. *When attempting
to put on the brakes the brake handle moves all the way back to the
stick grip. *We have repeatedly attempted to eliminate air in the
system by pumping .4 fluid up through the wheel cylinder drain
nipple. *We have sucked the system dry by vacuum applied, also to the
same nipple. *We have checked the nipple itself for blockage. *We
replaced the master cylinder. *We checked the cable to make sure there
was no slack yet the abbreviated handle plunger was virtually in
contact with the piston in the master cylinder and the master cylinder
piston was moving. *Nothing seems to make any difference. *IT

Sounds like you are doing everything right.
I assume you checked for wear of the pads? Easy to replace them and
always a good idea.
Also it is easy to replace the O-ring on the brake master cylinder.
However you would see seepage atounf the Master cylinder if it is
bad. I change them every few years because they do get old and hard.

good luck,
Dan
WO

We checked the cable to make sure there
was no slack yet the abbreviated handle plunger was virtually in
contact with the piston in the master cylinder and the master cylinder
piston was moving. *Nothing seems to make any difference. *

In addition to pad wear, discs get thinned over time as well. Make
sure the disc and pads are up to spec'd thicknesses. It is possible
the combo of both can run the piston out of useful travel. Also verify
the cable is transmitting full force, a frayed/worn out cable can have
enough strength to plunge the piston, but so much elasticity that it
won't do it with much force, especially if it's one of those wussy
bicycle cables and not the stout Boden (motorcycle) variety.

-Paul

On Mar 27, 10:58*am, sisu1a wrote:
We checked the cable to make sure there
was no slack yet the abbreviated handle plunger was virtually in
contact with the piston in the master cylinder and the master cylinder
piston was moving. *Nothing seems to make any difference. *

In addition to pad wear, discs get thinned over time as well. Make
sure the disc and pads are up to spec'd thicknesses. It is possible
the combo of both can run the piston out of useful travel. Also verify
the cable is transmitting full force, a frayed/worn out cable can have
enough strength to plunge the piston, but so much elasticity that it
won't do it with much force, especially if it's one of those wussy
bicycle cables and not the stout Boden (motorcycle) variety.

-Paul

Look at your caliper real close to verify that your line comes out the
very top of the piston cavity. If not you will need to make the line
as high as possible or even remove it and position it so the line is
high and then bleed again.

On Mar 27, 2:02*pm, glidergeek wrote:
On Mar 27, 10:58*am, sisu1a wrote:

We checked the cable to make sure there
was no slack yet the abbreviated handle plunger was virtually in
contact with the piston in the master cylinder and the master cylinder
piston was moving. *Nothing seems to make any difference. *

In addition to pad wear, discs get thinned over time as well. Make
sure the disc and pads are up to spec'd thicknesses. It is possible
the combo of both can run the piston out of useful travel. Also verify
the cable is transmitting full force, a frayed/worn out cable can have
enough strength to plunge the piston, but so much elasticity that it
won't do it with much force, especially if it's one of those wussy
bicycle cables and not the stout Boden (motorcycle) variety.

-Paul

Look at your caliper real close to verify that your line comes out the
very top of the piston cavity. If not you will need to make the line
as high as possible or even remove it and position it so the line is
high and then bleed again.

The hydraulic brake failed on my Discus 2 also a year or so ago and we
finally installed a repair kit on the master cylinder. We had lost
one of the o-rings and the fix worked perfectly. Bleeding the system
wasn't easy and we only got success after feeding fluid under pressure
from the slave.

i wonder if you effectively bled the system after installing the new
master cylinder?

Mike

Here my experience on my V2C 3U.
2 years ago, my brake was very tight and would respond immediately
with no slack.
Last season, I noticed brake fluid dripping from a drain hole in the
bottom of the fuselage.
Also my brake action deteriorated gradually.
I had not replaced the brake fluid (like I never do on my cars either)
and the fluid had gummed and was leaking around the master brake
cylinder. I replaced the original 20mm piston Magura master cylinder
with a new 16mm piston unit (mounted standard on BMW motorcycles) .
After extensive bleeding as described above, I still could not regain
real pressure.
(I realize that the smaller master piston does require more travel.)
However, at further inspection, I noticed that the brake pad on the
Cleveland caliper would withdraw upon release of the brake handle.
In other words, the caliper does not rest tight and at each brake
action fluid volume needs to be filled to bring the brake pads tight,
before brake pressure can be build up.
I decide to completely disassemble the Cleveland assembly to check for
gumming up and for overhaul.
Turns out there is hardly anything in the Cleveland assembly. Just one
standard O-ring.
New O-rings ordered. Caliper disassembled. Piston carefully pushed out
with a little airpressure from a small 12 V tire compressor.
It turned out that the aluminum caliper and piston had been corroded
substantially.
I presume from condensation moisture from high altitude flying and
mixing with the hydraulic fluid.
I lightly sanded, with 800 sand paper, the corroded section, where the
O-ring sits. Installed the new O-ring and re-assembled.
After again extensive bleeding (upwards from the caliper to the
reservoir), I now have pressure.
I still need to test fly to see how well the overhaul works.
I am not yet sure if this has resolve all problems as I now have
substantially more "squeeze" than before.
But as mentioned, this could be partly due to the smaller master
piston, which would give more throw but also more force/pressure.
Summarizing: My first problem was the leaking master cylinder. After
that next problem was piston in the Cleveland caliper retracting upon
brake lever release (instead of taking new fluid from the reservoir).
I am still not sure if this retracting is a problem of the new master
cylinder or a problem of the corroded Cleveland brake caliper.
3U

Hi Dick.

If you have checked everything, check it again! I think Mike is going in
the right direction and you still have air in the system.
If everything is ok then try this when bleeding the system.

With two people pump the handle to get maximum pressure, your assistant
then opens the bleed nipple forcing the fluid out, hold the leaver until
the nipple is closed then slowly release the leaver, wait 30 seconds then
repeat. Hopefully you will feel it improving after 4 or 5 pumps and don't
forget to top up as you do this.

Regards

Brian

On Mar 27, 9:34*am, Dick wrote:

We have sucked the system dry by vacuum applied, also to the
same nipple.

I assume you actually didn't mean that since sucking the system dry
ensures that it is totally filled with air unless you used a high
vacuum pump.

Getting a high flow rate using either suction or pressure usually
works but you need a fluid reservoir large enough to sustain the
flow. My PA28-180 has 5 master cylinders and 2 slave cylinders and is
a real bitch to bleed after the system has been opened. I used a pump
up garden sprayer to feed fluid to the caliper bleed nipples and used
a large bottle to catch the overflow from the reservoir.

So far I've had no problem with the hydraulic brake on my 28 so no
experience with that yet.

Andy

On 3/28/2011 1:46 AM, weersch wrote:

But as mentioned, this could be partly due to the smaller master
piston, which would give more throw but also more force/pressure.
Summarizing: My first problem was the leaking master cylinder. After
that next problem was piston in the Cleveland caliper retracting upon
brake lever release (instead of taking new fluid from the reservoir).
I am still not sure if this retracting is a problem of the new master
cylinder or a problem of the corroded Cleveland brake caliper.

I had a similar problem with my Cleveland brake system on my ASH 26E. It
worked fine for years, but one day it was very "spongy" after rigging. I
loosened the cap on the fluid reservoir, and in just two brake
applications, it was working fine. I cleaned the cap and the vent in it,
and have had no further problems in the seven years since then.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

On Mar 27, 10:58*am, sisu1a wrote:


It is possible the combo of both can run the piston out of useful travel.

Don't see how that is possible. Hydraulic disk brake systems are self
compensating for wear. As the pads and disk wear the system fluid
volume increases and fluid transfers from the master cylinder
reservoir when the piston is in the retracted position. There is no
limit on the piston travel of a Cleveland caliper. It just keeps
going until it is ejected from the O ring seal.

Andy